The present invention relates generally to the control of dust laden air in material handling operations and, more particularly, to the control and abatement of dust in the loading of particulate materials in large hoppers of the type generally employed at marine terminals, rail terminals and like high tonnage bulk material transfer centers. Conventionally, in the unloading of particulate materials from cargo holds of ships, from rail cars, storage bins and such bulk receptacles, the particulate cargo is transferred from the receptacle by various means, such as, clamshell buckets, conveyor belts, car dumpers, front end loaders and the like, and the material is then dumped into a receiving hopper which directs the material to a take-away system in the form of a conveyor belt, truck or the like. When certain types of bulk materials are discharged by gravity into the hopper, large clouds of dust laden air are emitted into the surrounding environment. This air pollution problem has received very close attention in terminals located near populated areas and many operations are threatened with monetary fines, reduced tonnages, or outright shut-down, if the nuisance is not abated or controlled to acceptable levels.
The size of receiving hoppers varies, and is usually determined more by the size of the equipment filling the hopper rather than by the volume of bulk material to be discharged into it. Clamshell buckets, front end loaders, trucks, railroad cars and such, deliver the bulk material to the receiving hopper and, as such, the hopper dimensions must exceed the physical dimensions of these pieces of equipment. These oversized dimensions are needed in order to satisfy the generally expected misalignment of the loading equipment relative to the hopper due to bucket swing, overshooting, reach, operator adeptness, to name a few. Thus, the volume of material being handled is relatively small when compared with the volume of the hopper. This excessive, open space within the hopper results in random flow patterns of displaced air when the material is dumped which permits the escape of fugitive dust clouds into the surrounding environment.
In one conventional dust collection system which has been developed in an attempt to control dust emission problems in receiving hoppers, an air suction system is placed around the hopper in an attempt to draw in all of the rapidly rising fugitive dust streams. These intake duct systems must be installed in close proximity to, but spaced from the potential flow lines of the dumped material. The large physical size of the hoppers dictates that this location be safely fixed around the perimeter of the upper rim of the hopper. The negative draft influence of these conventional intake ducts is very limited since the influence of the negative draft decreases by the square of the distance from the duct. Thus, these prior systems are rendered ineffective when attempting to collect displaced dust laden air leaving the central regions of the hopper at high flow velocities. Massive air movement is required to increase the dust collecting efficiency of these prior devices but that can only be realized by greatly increasing the fan capacity. The viability of this approach is negated by the correspondingly high equipment costs and increased operating expenses resulting from the increase in the fan horsepower requirements.
It is also known to employ vertically extending barriers around three sides of a hopper so as to create a wind screen in an effort to diminish the effect of cross-winds on the escaping dust clouds. Naturally, this approach to dust emission control is not totally satisfactory since the hopper itself is still free to generate fugitive dust.
My invention solves these problems by providing a dust control system for hoppers which is elegantly simple, relatively inexpensive to construct and cost efficient to operate. My invention provides a dust control method and apparatus for hoppers in which the displaced air carrying the generated dust in the hoppers is totally captured. The dust control system of the present invention provides a hopper with restricted material and air flow paths in which displaced air is directed towards an isolated region within the hopper which contains the dust collection devices. By capturing the displaced air and dust within the hopper area, the volume of air and required fan horsepower are kept to a minimum due to the confined space involved. Thus, the present invention provides a dust control system for receiving hoppers in which both capital and operating costs are lowered due to the decreased horsepower requirements, while dust collection efficiency is dramatically increased as compared with conventional dust control systems.